As energy problems have attracted increasing attention in recent years, there has been a demand for a power source having a higher energy density and involving clean emissions. A fuel cell is a power generator having an energy density several times as high as that of the existing battery, and is characterized in that it has a high energy efficiency, and it is free from, or reduced in, nitrogen oxides or sulfur oxides contained in an emission gas. Thus, the fuel cell can be said to be a very effective device fulfilling requirements for a next-generation power source device.
With such a fuel cell, methanol or hydrogen is used as a fuel. To supply such a fuel continuously responsive to the consumption of the fuel, a pressure regulating valve is necessary. To achieve downsizing of the fuel cell, the pressure regulating valve needs to be downsized.
With the fuel cell which obtains an electromotive force by an electrochemical reaction between hydrogen and oxygen, hydrogen is required as a fuel. A known example of a facility for generating a hydrogen gas is a hydrogen generating facility of a structure which has a reaction vessel accommodating a metal hydride (boron hydride salt), and a water tank, and in which water within the water tank is supplied to the metal hydride in the reaction vessel by a pump (see, for example, Patent Document 1).
In such a hydrogen generating facility as well, a pressure regulating valve is required for supplying water into the reaction vessel in accordance with the consumption of hydrogen. Such a pressure regulating valve similarly needs to be downsized.
For the pressure regulating valve in a fuel cell system as mentioned above, a proposal has been made for a control mechanism which controls the amount of the fuel supplied from a fuel tank by utilizing a differential pressure between the pressure of a fuel electrode chamber and the pressure of an oxygen electrode chamber or outside air (see Patent Document 2).
The pressure regulating valve of this document, however, poses the problem that since a valve element acting in response to the differential pressure undergoes the pressure from the fuel tank, it fails to act normally unless the internal pressure of the fuel tank is constant. Such a document naturally targets the fuel cell using a hydrogen absorbing alloy, which presents a region where the hydrogen desorption pressure becomes constant. Thus, the above problem is supposed not to grow to a serious problem. On the other hand, the aforementioned hydrogen generating facility involving great changes in pressure, for example, suffers from the problem that the pressure regulating valve cannot be used.
In fields other than the above-mentioned fuel cell system and hydrogen generating facility, too, there is an intense demand for the advent of a pressure regulating valve which is compact and controllable without being supplied with electric power, and whose operating pressure can be set easily.
Patent Document 1: JP-A-2002-137903
Patent Document 2: JP-A-2004-31199